The objective of this work is to synthesize derivatives of steroid hormones labeled with gamma emitting isotopes and evaluate these derivatives as biological tracers. The biologically active steroid will be derivatized so that it contains a radionuclide carrying group; if the radionuclide carrying group is a chelating agent, the chelating portion of the resulting derivative will be designed to retain high affinity for a metallic radionuclide such as Tc-99m. If the radionuclide is iodine it will be bound to an aromatic ring or an ethynyl group added to the structure of the biologically active compound. The overall aim is a thorough and fundamental investigation of a small number of well chosen derivatives. As in the previous proposal the major emphasis will be placed on estrogen derivatives. The development of such a derivative will allow, by external detection, production of an image of the spatial distribution of the steroid in patients with steroid dependent malignancy.